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March 10, 1964 D. L. GRAHAM ETAL 3,124,626

PROCESS FOR PRODUCING BOAT HULLS OF SANDWICH CONSTRUCTION Filed Sept. 6,

IN VENTORS United States Patent 3,124,626 PROCESS FOR PRODUCING BOATHULLS 0F SANDWICH CONSTRUCTION Donald L. Graham and James A. Strnthers,Jr., Midland,

Mich, assignors to The Dow Chemical Company, Midland, Mich, acorporation of Delaware Filed Sept. 6, 1960, Ser. No. 54,169 8 Claims.(Cl. 26445) This invention relates to a molding process and moreparticularly to a molding process by which boat hulls of sandwichconstruction may be produced economical- 1y.

Boats formed of sandwich construction have many desirable features suchas, high strength to weight ratio, stiffness, and built-in buoyancy.However, such type boats made according to the methods of the prior artgenerally require numerous fabrication steps employing a great amount ofhand labor. Consequently, the quality and uniformity of the finishedmolded boat product depends largely upon the skill of the individualworkman.

The process of the present invention utilizes the basic technique andcompositions of the copending patent applications of: Robert F. Newbergand Ritchey 0. Newman, Jr., Serial No. 791,301, filed February 5, 1959,which issued on November 8, 1960, as Patent No. 2,95 8,- 905; and DonaldL. Graham, Robert N. Kennedy, and Earle L. Kropscott, Serial No.562,122, filed January 30, 1956, which issued on November 8, 1960, asPatent No. 2,959,508. However, the present disclosure sets forth indetail, and with certain additional steps, how such basic process may beused in making boat hulls in an efiective and economical manner.

The boat hull molding process of the present invention reduces thenumber of fabrication steps as compared with methods of the prior artfor producing molded boat hulls. Furthermore, it provides high qualityand uniformity of finished boat hulls which do not depend pri marilyupon the skill of the workman.

Briefly, the process of the invention involves the following steps: (a)providing a male mold and a female mold having contoured surfaces ofdesired finished boat hull shape; (b) applying mold release to thesurfaces of both molds; (c) applying gel coat to both surfaces of themold; (d) allowing the gel coat surface to cure to a tacky state; (e)applying a reinforcing material, such as glass cloth, to the tacky gelcoated surfaces; (1) closing the molds to form a mold cavity; (g)introducing prefoamed thermoplastic expandable beads into the moldcavity; (h) injecting a mixture of epoxy resin curing agent and modifierinto the bead-filled cavity; (i) allowing time for a chemical reactionwhich develops exothermic heat to cause expansion and setting of thethermoplastic beads and, advantageously, impregnation of the reinforcingmaterial with reacted epoxy resin forced therein by the expanding actionof the beads, and (j) separating the mold halves to remove the resultingmolded boat hull. In some cases, it may be advantageous for step (g) topartially or completely precede step (f), depending on the particularsequence of operations and bead charging procedure desired to befollowed.

The main object of this invention is to provide a molding process forproducing boat hulls of sandwich construction in an economical manner.

Another object of this invention is to provide a molding process forproduction of boat hulls which reduces the number of fabrication steps.

Still another object of this invention is to provide a molding processfor the production of boat hulls of sandwich construction of highquality and uniformity.

A further object is to produce a boat hull of sandwich constructionhaving a light weight rigid core, and a plastic skin covering on theexterior surfaces of the core, wherein the plastic network extendingthrough and reinforcing the core is also saturated into and impregnatesthe weave or intersticial texture of the reinforcing materialconstituting the cover for the core.

Still another object of the invention is to provide a molding processfor producing boat hulls of sandwich construction which process does notprimarily depend upon manual skills.

These and further objects and features of the invention will become moreapparent from the following description and accompanying drawingswherein:

FIG. 1 is a side elevation view illustrating in separated position twomolds used for practicing one embodiment of the process of theinvention;

FIG. 2 is a plan view of the molds shown in FIG. 1;

FIG. 3 is an enlarged section view generally as seen along line 33 inFIG. 2;

FIG. 4 is an enlarged fragmentary section view generally as seen alongline 4 4 in FIG. 2;

FIGS. 5 to 9, inclusive, are illustrations depicting various stages inthe process of the depicted embodiment of the invention for the moldingof a boat hull;

FIG. 10 is a plan view showing a lower mold arranged according to amodified embodiment of the invention;

FIG. 11 is an enlarged section view generally as seen along line 11-11in FIG. 10; and

FIG. 12 is a section view as seen along line 12--12 in FIG. 11.

Referring now to the drawings, and more particularly to FIG. 1, thenumeral 10 identifies a lower mold sec tion, while numeral 12 identifiesan upper mold section. The lower mold section includes a wall portion14, the inner surface of which is curved, to provide a molding form forthe exterior surface of a boat hull to be molded thereby, while theupper mold section includes a wall portion 16, the outer surface ofwhich is curved to provide a molding form for the interior surface of aboat hull to be molded thereby. As best seen in FIG. 3, the wall 14 ofthe lower mold includes a horizontal flange 18 arranged about the entireupper periphery, while the wall 16 of the upper mold has a horizontalflange 29 which extends around the entire upper periphery of the curvedwall.

When the upper mold section 12 is lowered into the lower mold section 10so that the horizontal flange 20 seats upon the horizontal flange 18' ofthe lower mold section, a space, or cavity 22 (FIG. 4) will be providedbetween the walls 14 and 16. Such cavity 22 is designed to provide thedesired thickness and configuration of a boat hull to be molded therein.Plate, or shim means 23 placed upon the flanges 18 and 20, may be usedfor regulation of bull thickness.

For the purpose of maintaining predetermined cavity dimensions,indexing, or locating pins 24- are secured to the upper mold flange 2i)and proiec-t downwardly for entry within holes 26 formed in the lowermold flange 18.

While the lower and upper mold sections 10 and 12 respectively may bemade of various materials, the sections are preferably formed ofaluminum. Such material has the necessary strength, is readily cast andmachined, has good thermo-conductance, and is of light weight whichmakes for easy handling of the mold sections. In forming the moldsections, .a continuous tubing, or pipe means 28 is arranged in thewalls of each section which pipe means is used for circulating heatingand cooling medium, such as water, through the mold sections asrequired. A mold preheating temperature of approxi- 3 are completed andin preparation for mold opening and finished hull removal.

Water enters the pipe mean-s 2 in the lower mold sect-ion via a pipe, orhose 3t). After circulating through the pipe means in the lower mold,the water flows through a pipe, or hose 32 to the upper mold sect-ionwhere it passes through the pipe means 28 thereof and exits through apipe, or hose 34 back to the source, or a drain, as required. A pipe 36is arranged on each mold section for feeding compressed air through themold walls 14 and 16 via a plurality of short pipes 38, so as to easethe parting force developed by the sticking of the finished hull and thevacuum build up during separation.

In one embodiment of the invention, as illustrated, a plurality ofopenings, or holes 40 are provided in the upper mold section wall 16 andin the keel line for charging all materials to the mold cavity 22. Theseholes are each closed with a removable plug 42 maintained in position bya leaf spring clamp 44. Eyelets 46 are secured to the upper surface ofthe flange 29, for attachment of chains 48, whereby the upper mold section 12 may be moved as required. Frame means t as well as support ribs,or plates 52, are arranged for maintaining the lower mold wall portion14 in position. Bolt means (not shown) may be used to secure the moldsections together during molding operation.

The apparatus as above described may he used to practice the process ofthe invention, the steps of one embodiment of which are as follows:

(1) A mold release material is applied to the surface of the mold cavityWalls 14 and :16 of the mold sections, such material being of the typecommonly used for this purpose, as for example, wax, or polyvinylalcohol, or a combination of both.

(2) A gel coa is next applied over the mold surfaces which have beentreated with the release material which may be applied by brush, orspray (FIG. 5). The gel coat, which may be :a polyester, or epoxy resin,is then allowed to cure to a tacky state. With air inhibiting polyesterresins, the surface will remain tacky for a considerable period of time(if not indefinitely) until air is excluded from it, or until subsequentfoaming resins, or laminating resins are applied to it.

Suitable gel coats are of the variety known to the art for suchpurposes. For example, a good polyester gel coat for use in practice ofthe present invention is comprised of the reaction product of about 1.2moles of propylene glycol with a mixture of 0.5 mole of maleic anhydrideand 0.5 mole phthalic ranhydride dissolved in 20 to 40 weight percent,based on composition Weight, of styrene monomer (preferably about 35weight percentstyrene) and containing about 50 weight percent ofcombined conventional extender, filler and pigment including about 3weight percent of an expanded silica (such as Cab-O-Sil) as athixotropic agent. The polyester composition is cured with about 1weight percent of a peroxide, such as methyl ethyl ketone peroxide, inthe gel coat formulation.

A satisfactory epoxy gel coat is made from the reaction product ofBisphenol A and epichlorohydrin having an epoxy equivalent weight ofabout 190. To this is :added about 10 weight percent, based on gel coatcomposition weight, of butyl glycidyl ether as a reactive diluent. Thesame extender, filler, pigment systems (including the expanded silica)as above described is utilized in about the same proportion asindicated. The epoxy gel coat is cured with about 11 parts. by weight100 parts of the resin/ diluent combination of a conventional epoxycuring agent, such as diethylene triamine.

(3) A reinforcing material is then placed uniformly over the tacky gelcoat surface (FIG. 6). The reinforc ing material may be glass cloth,woven rovings, glass m at, sisal mat, needled mat, synthetic fibers, orother materials as employed in reinforced plastic work. A doublethickness of reinforcing material may be placed ii in high stress areasof the hull, such as in the corners and on the transom and bow.

The gel coated surface presents an ideal base for Wall papering onreinforcing materials, since it provides necessary support to make thematerial conform and adhere to the mold contours, yet does not saturatethe weave, texture or openings in the material.

In placing the reinforcing material it will be necessary to formopenings therein which coincide with all of the charging openings 40when such method of operation is employed. Such openings may be patchedlater when the molded boat hull is removed from the molds, if necessaryor desirable. To minimize such patching, the charging ports may be keptto a minimum, employing only enough to readily charge the mold cavitywith expandable bead filler.

(4) The upper mold section 12 is then placed into the lower mold section10 so that the flange 20 seats upon the flange 18, thus providing theenclosed cavity 22; expandable thermoplastic prefoamed beads, and/ orgranules, of a density, say of 4#/ft. are put into the cavity. Thesebeads are capable of further expansion. The cavity charging may be donefor example, by the use of pneumatic blowing equipment (FIG. 7). Or, ifpreferred, the beads (as has been indicated) may be completely chargedto the mold before its closing or the bulk of the total charge added atsaid point with the remainder introduced through charge ports. Suchbeads are preferably polystyrene or modified styrene polymer granules ofthe type known under the trademark Pelaspan as are obtainable from theDow Chemical Company, Midland, Michigan.

(5) A mixture of epoxy resin, polyarnine curing agent, and modifier isnext pumped, or forced into the bead filled cavity via some of theopenings 40. The exothermic heat which is developed from the chemicalinteraction of the epoxy resin and polyarnine curing agent causesexpansion of the expandable thermoplastic beads. The expansion of thebeads and the accompanying pressure development from such expansion,forces the reaction components throughout the beads in the mold cavity.Such distribution pressure force progressively brings the reactioncomponents in contact with more expandable beads, which are thusexpanded and force the reaction components onward in the cavity.Finally, as the expandable beads are fully enlarged and knit togetherforming a solid light weight core, the epoxy resin is forced to theoutside where it saturates the reinforcing material with resin. Eachresulting reinforced laminate thus produced is bonded on one side to thegel coat, and to the foamed core on the other side (FIG. 8). Asindicated, the so-called exothermus epoxy resin agent which foams thebeads to their finally expanded form provides an interlacing networkthroughout the expanded plastic granules which extend to and through, insaturating interstice impregnating contact with, the reinforcing layerof glass cloth or the like.

The composition thus produced 54 (FIG. 9) is strong, of light weight,and excellently suitable for boat hull construction.

If desired, particularly when a minimum of cavity openings are to beemployed, the entire cavity may be filled with both beads andself-reacting epoxy resin exothermus agent through one or more (usuallythree or four) charge ports disposed (generally about equispaced buthowever may be preferred) in and through the lower mold section 10 alongthe keel line. Actually, excellent results can be achieved with only asingle charge port in the mold (either upper or lower), especially whenpneumatic bead injection and probes (as hereinafter described) for epoxyresin distribution are employed. In this Way all or any desired portionof the illustrated openings 44 can be dispensed with.

Alternatively, the epoxy resin agent can be added to the bead filledmold cavity (charged with beads full before closing or in any efficientway through one or more charge openings) through tubes or probes (eitherperforated or merely open ended, or both) disposed in the cavity priorto closing. One or more such probes may be employed, with two or threebeing frequently suitable, so long as they are disposed to efficientlyinterject and disperse the epoxy resin agent in the mold cavity. Suchprobes for pressuring the exothermus agent to the beads mayadvantageously be left within the core after the foaming operation,since they generally do not materially degrade or weaken the resultingstructure. Advantageously, in such instances, the probes are made of aplastic material, such as polyethylene tubing, which is flexible andactually is compressed to be all or nearly fiat or interiorly closedupon expansion of the beads. Of course, pressure probes of rigidmaterials, including metals, may also be employed.

Good results with probes are obtained in a boat hull construction using/2 I.D.-%" O.D. polyethylene tubing as probes having spiral perforations55 on 1" centers using 120 rotation per hole. Three such tubes may beused as seen in FIG. 10. One tube 58 is layed along the keel of a lowerhull mold 57 and extends for about the entire length thereof, being fedfrom the fore or after section of the hull mold 57 but advantageouslythrough an aperture in the bow from a charging pot 59. Two other tubes60 and 62 are layed lengthwise of the hull mold about along the gunwales(in smaller units) or, at any rate, about equidistant between the heeland upper edge of the mold cavity. Prior to laying the tubes 58, (it?and 62, the upper and lower molds are prepared by covering with arelease coat, and a gel coat, following which a reinforcing material,preferably glass cloth, is placed thereupon. Expandable thermoplasticpreformed beads are placed in the lower mold 57 so that the tubes arecompletely covered. The upper half of the hull mold (not shown) is thenplaced in position upon the lower mold thus forming a cavity having theshape of a boat hull. If necessary, additional preformed beads may befed into the cavity by pressurized probes (not shown). The assemblage isnow ready for charging with an epoxy resin agent. With such a set-up, itis beneficial to add the first portion of epoxy resin mixture throughthe keel tube 58 (using enough to foam the beads in the bottom part ofthe mold) then, sequentially, to add the rest through the outer tubes 6dand 62. This ensures excellent foaming and expanding action in the upperside portions of the hull and achievement of uniform, premium qualityconstruction.

A hull made according to the invention, which may be damaged in use, canbe quickly repaired by use, for example, of high density foamed materialcemented in place with a quick drying (or other) cement, following whicha layer of fiberglass cloth or other reinforcement impregnated with afast hardening epoxy resin is placed over the foamed material andallowed to cure.

(6) The upper mold section 12 is then lifted out of the lower moldsection it). Compressed air is advantageously directed at this timethrough the pipes 36 to cause separation of a formed boat hull 56 fromthe molding surfaces of the upper and lower molds.

It will be apparent from the foregoing that the process of the inventionprovides fabrication of boat hulls of sandwich construction in a veryeconomical manner, and which process satisfies all the objectives ashereinbefore set forth. It may be added that by the process of theinvention, various kinds of surfaces and inserts may be easily bonded tothe hull during the molding thereof.

The foregoing description has been given in detail without thought oflimitation since the involved inventive principles, as is apparent froma reading of the specification, are capable of assuming other formswithout departing from the spirit of the invention or accompanyingclaims.

What is claimed is:

1. A process for producing a boat hull of sandwich construction with anouter plastic skin covering and a lightweight rigid core of beadedexpanded thermoplastic material, comprising the. steps of forming alower mold section with an inner curved surface to provide a mold formfor the exterior surface of a boat hull and an upper mold section withan outer curved surface to provide a mold form for the interior surfaceof said boat hull, each of said sections having means therein forreleasing the boat hull from said sections after molding, and inletmeans for charging the mold cavity formed when the mold sections areplaced together, applying mold release material to said inner and saidouter curved surfaces respectively, followed by application of a gelcoat, allowing the gel coat to become tacky, applying a reinforcingmaterial over the tacky gel coat, placing the mold sections together toform a mold cavity, charging prefoamed expandable thermoplastic beadsinto said mold cavity via said inlet means, then injecting anexothermous epoxy resin mixture via said inlet means into the beadcharged cavity, said exothermous resin mixture chemically interactingwith evolution of heat which causes further expansion and final settingof the prefoamed beads to produce a boat hull having a solid lightweightcore with epoxy impregnated reinforcing material embedded on theexterior surfaces as a plastic skin covering, and removing the boat hullfrom the mold cavity utilizing the release means in said lower and uppermold sections.

2. The process of claim 1, wherein the mold release material comprises acombination of wax and polyvinyl alcohol.

3. The process of claim 1 wherein the gel coat comprises a reactionproduct of propylene glycol, maleic anhydride, phthalic anhydride andstyrene monomer.

4. The process of claim 1 wherein the gel coat comprises a reactionproduct of biphenol and epichloryhydrin.

5. The process of claim 1 wherein the reinforcing material comprisesglass cloth.

6. The process of claim 1 wherein the expandable thermoplastic beadscomprise polystyrene.

7. A process for producing a boat hull of sandwich construction with anouter plastic skin covering and a lightweight rigid core of beadedexpanded polystyrene, comprising the steps of forming a lower moldsection with an inner curved surface to provide a mold form for theexterior surface of said boat hull and an upper mold section with anouter curved surface to provide a mold form for the interior surface ofsaid boat hull, each of said sections having means therein for releasingthe boat hull from said sections after molding, and inlet means forcharging the mold cavity formed when the mold sect1ons are placedtogether and a perforated charging tube communicating with said inletmeans, applying a mold release to said inner and outer curved surfacesrespectively, followed by application of a gel coat, allowing the gelcoat to become tacky, applying a reinforcing material over the tacky gelcoat, placing expandable polystyrene beads in the lower mold section toenclose said perforated charging tube, placing the mold sectionstogether to form a mold cavity, introducing prefoamed expandablepolystyrene beads into the mold cavity via said inlet means and saidcharging tube, then injecting epoxy resin, polyamine curing agent, andmodifier via said inlet means and said charging tube into the beadcharged cavity, said resin, curing agent and modifier chemicallyinteracting with the evolution of heat to cause further expansion of theprefoamed beads thereby forcing at least a portion of the epoxy resininto and through the interstices of the reinforcing material to producea boat hull having a solid lightweight core with epoxy impregnatedreinforcing material as a plastic skin covering, and removing the boathull from the mold cavity utilizing the release means in said lower andupper mold sections.

8. The process of claim 7 wherein the charging tube in repetitivepattern along its length.

References Cited in the file of this patent UNITED STATES PATENTSNiessen et a1. Feb. 5, 1946 Collins Aug. 2, 1949 Halsall Oct. 21, 1952Simon et a1 Dec. 27, 1955 Kelley May 29, 1956 Leverenz Aug. 13, 1957Bickel et a1. Dec. 24, 1957 Brown Oct. 4, 1960 Newberg et a1. Nov. 8,1960 Graham et al. Nov. 8, 1960 Gould Mar. 28, 1961 Reeves July 25, 1961Fisher Dec. 19, 1961 FOREIGN PATENTS Great Britain Dec. 28, 1956

1. A PROCESS FOR PRODUCING A BOAT HULL OF SANDWICH CONSTRUCTION WITH ANOUTER PLASTIC SKIN COVERING AND A LIGHTWEIGHT RIGID CORE OF BEADEDEXPANDED THERMOPLASTIC MATERIAL, COMPRISING THE STEPS OF FORMING A LOWERMOLD SECTION WITH AN INNER CURVED SURFACE TO PROVIDE A MOLD FORM FOR THEEXTERIOR SURFACE F A BOAT HULL AND AN UPPER MOLD SECTION WITH AN OUTERCURVED SURFACE TO PROVIDE A MOLD FORM FOR THE INTERIOR SURFACE OF SAIDBOAT HULL, EACH OF SAID SECTIONS HAVING MEANS THEREIN FOR RELEASING THEBOAT HULL FROM SAID SECTIONS AFTER MOLDING, AND INLET MEANS FOR CHARGINGTHE MOLD CAVITY FORMED WHEN THE MOLD SECTIONS ARE PLACED TOGETHER,APPLYING MOLD RELEASE MATERIAL TO SAID INNER AND SAID OUTER CURVEDSURFACES RESPECTIVELY, FOLLOWED BY APPLICATION OF A GEL COAT, ALLOWINGTHE GEL COAT TO BECOME TACKY, APPLYING A REINFORCING MATERIAL OVER THETACKY GEL COAT, PLACING THE MOLD SECTIONS TOGETHER TO FORM A MOLDCAVITY, CHARGING PREFOAMED EXPANDABLE THERMOPLASTIC BEADS INTO SAID MOLDCAVITY VIA SAID INLET MEANS, THEN INJECTING AN EXOTHERMOUS EPOXY RESINMIXTURE VIA SAID INLET MEANS INTO THE BEAD CHARGED CAVITY, SAIEXOTHERMOUS RESIN MIXTURE CHEMICALLY INTERACTING WITH EVOLUTION OF HEATWHICH CAUSES FURTHER EXPANSION AND FINAL SETTING OF THE PREFOAMED BEADSTO PRODUCE A BOAT HULL HAVING A SOLID LIGHTWEIGHT CORE WITH EPOXYIMPREGNATED REINFORCING MATERIAL EMBEDDED ON THE EXTERIOR SURFACES AS APLASTIC SKIN COVERING, AND REMOVING THE BOAT HULL FROM THE MOLD CAVITYUTILIZING THE RELEASE MEANS IN SAID LOWER AND UPPERMOLD SECTIONS.